1. Field of Invention
The present invention relates to a radio-controlled timepiece that receives a standard time signal containing time information and adjusts the time based on the received standard time signal, and to a control method for the radio-controlled timepiece.
2. Description of Related Art
Radio-controlled timepieces that can receive a standard time signal are known from the literature. See, for example, Japanese Unexamined Patent Appl. Pub. JP-A-H10-274681, and Japanese Unexamined Patent Appl. Pub. JP-A-2006-60849.
The standard time signal is an amplitude modulated signal, and the reception circuit of the radio-controlled timepiece has a filter or other unit of extracting the envelope of the received signal, and an analog/digital conversion circuit that compares the envelope signal with a reference voltage by unit of a comparator to digitize the envelope signal. The radio-controlled timepiece acquires time information and displays the time based on the time code signal obtained by the A/D conversion circuit.
The radio-controlled timepiece also typically has an automatic gain control (AGC) circuit to automatically control the amplification factor of the reception signal based on the reception signal.
While the radio-controlled timepiece has an AGC circuit, the threshold values used by the A/D conversion circuit for digitizing the signal are fixed, and the reception environment may therefore prevent acquiring the correct time code.
As a result, the radio-controlled timepiece receives the standard time signal continuously for three to seven minutes in order to acquire the time code multiple times, and then compares and evaluates the received time codes to determine if the correct time information was received.
This method therefore necessarily requires several minutes in order to determine if the correct time information was received. This unit that a relatively long time is required to determine that the correct time information cannot be acquired if the reception environment is poor, and power consumption increases accordingly